1. Field of the Invention
The present invention relates to a clamp apparatus capable of clamping a workpiece by using an arm which is rotatable by a predetermined angle in accordance with a driving action of a driving mechanism.
2. Description of the Related Art
The clamp cylinder has been hitherto used, for example, in order to clamp a constitutive part when the constitutive part of an automobile or the like is welded. Such a clamp cylinder is disclosed, for example, in U.S. Pat. No. 4,458,889.
The clamp cylinder disclosed in U.S. Pat. No. 4,458,889 is shown in FIGS. 22 and 23. A piston rod 2 is arranged movably back and forth between a pair of dividable bodies 1a, 1b. A coupling 3 is connected to one end of the piston rod 2. A pair of links 5a, 5b and a pair of rollers 6a, 6b are attached rotatably by the aid of a first shaft 4 on both sides of the coupling 3 respectively. An arm 8, which is rotatable by a predetermined angle, is connected between the pair of links 5a, 5b by the aid of a second shaft 7.
In this arrangement, the pair of rollers 6a, 6b are provided rotatably by the aid of a plurality of needles 9a installed to a hole. The piston rod 2 is provided so that it is displaced integrally with the rollers 6a, 6b in accordance with the guiding action of the rollers 6a, 6b which make sliding movement along track grooves 9b formed on the bodies 1a, 1b respectively.
However, the clamp cylinder disclosed in U.S. Pat. No. 4,458,889 concerning the conventional technique described above involves the following inconvenience. That is, when an unillustrated workpiece is clamped by the arm 8, the clamping force is decreased due to the change of the angle of rotation of the arm 8.
In the case of the clamp cylinder described above, the reaction force, which is generated when the workpiece is clamped by the arm 8, is applied to the first shaft 4. Therefore, it is necessary to design the diameter of the first shaft 4 considering, for example, the surface pressure and the strength. As a result, an inconvenience arises in that the diameter of the first shaft 4 is increased.
Further, it is necessary to design the wall thickness and the diameter of the rollers 6a, 6b considering the surface pressure and the strength of the pair of rollers 6a, 6b which make sliding movement along the track grooves 9b. As a result, the following inconvenience arises. That is, the shape of the pair of rollers 6a, 6b is increased, in accordance with which the size of the bodies 1a, 1b is increased.
A general object of the present invention is to provide a clamp apparatus which makes it possible to maintain a substantially constant clamping force even when the angle of rotation of an arm is changed when a workpiece is clamped.
A principal object of the present invention is to provide a clamp apparatus which makes it possible to decrease the diameter of a knuckle pin by receiving the reaction force generated upon the clamping by using a guide roller.
Another object of the present invention is to provide a clamp apparatus which makes it possible to realize a small size of a body.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.